GolangでAES256 CBCモードで暗号化 & 復号するサンプルコード

aes-256-cbc.go

package library

import (
	"bytes"
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
)

type Encryption struct {
	block cipher.Block
}

type EncryptedContext struct {
	Iv         []byte
	CipherText []byte
}

func NewEncryption(key string) (*Encryption, error) {
	block, err := aes.NewCipher([]byte(key))
	if err != nil {
		return nil, err
	}

	return &Encryption{
		block: block,
	}, nil
}

func (e *Encryption) Encrypt(message string) (*EncryptedContext, error) {
	r := make([]byte, e.block.BlockSize())
	if _, err := rand.Read(r); err != nil {
		return nil, err
	}

	iv := r[:e.block.BlockSize()]
	paddedMessage := e.paddingByPKCS5([]byte(message), e.block.BlockSize())
	cipherText := make([]byte, len(paddedMessage))

	encrypter := cipher.NewCBCEncrypter(e.block, iv)
	encrypter.CryptBlocks(cipherText, paddedMessage)

	return &EncryptedContext{
		Iv:         iv,
		CipherText: cipherText,
	}, nil
}

func (e *Encryption) Decrypt(cipherText []byte, iv []byte) string {
	paddedMessage := make([]byte, len(cipherText))

	decrypter := cipher.NewCBCDecrypter(e.block, iv)
	decrypter.CryptBlocks(paddedMessage, cipherText)

	return string(e.unPaddingByPKCS5(paddedMessage))
}

func (e *Encryption) paddingByPKCS5(message []byte, blockSize int) []byte {
	needed := blockSize - len(message)%blockSize
	padding := bytes.Repeat([]byte{byte(needed)}, needed)

	return append(message, padding...)
}

func (e *Encryption) unPaddingByPKCS5(cipherText []byte) []byte {
	onePadding := cipherText[len(cipherText)-1]

	return cipherText[:len(cipherText)-int(onePadding)]
}